Education: Ph.D. University of Western Ontario, Canada

C-H and C-C bond activation and functionalization Chemical structures, dynamics, and mechanisms Laser electron and ion spectroscopy Photoelectron velocity-map imaging Infrared-ultraviolet ionization spectroscopy Mass spectrometry Laser-assisted reaction and synthesis Computational Chemistry The development of inorganic and organometallic chemistry has enabled chemists to generate and organize a large amount of information about stable metal compounds. In contrast, chemists know much less about reactive, unstable metal species. Although the stable compounds are starting materials in chemical synthesis and catalysis, the active agents and key intermediates in these processes are the reactive species. These species are hard to isolate and characterize experimentally because they are short-lived and difficult to describe theoretically because they are electronically complex. Research in our group focuses on the detection and characterization of the reactive chemical substances formed in metal-promoted hydrocarbon and biomolecule activation reactions. Our goals are to come up with general rules or concepts that can be used to predict the formation, structures, and properties of such species present in catalytic processes.

We develop and use a variety of spectroscopic and imaging methods to characterize transient metal-containing substances. These methods include mass spectrometry, pulsed field ionization-zero electron kinetic energy (ZEKE), mass analyzed threshold ionization (MATI), infrared-ultraviolet (IR-UV) resonant photoionization, and photoelectron velocity-map imaging. At the risk of oversimplification, our experiments involve using a laser and a gas expansion to create super cold gaseous particles at a temperature of hundreds of degrees Fahrenheit below zero and flying at a speed of some 3000 miles per hour. A second laser is then shot into the gas jet to remove an electron from a metal-containing substance and produce a positively charged ion directly, or to excite the substance to a high energy state followed by ionization with a carefully shaped electrical pulse. The whole process takes a tiny fraction of a second. The electrons or ions are captured by a very sensitive particle detector or imaged by a high-tech charge-coupled device digital camera. The electron and ion signals are stored in a laboratory computer for data analysis. These techniques not only offer high spectral resolution, but also provide the ability to study chemical intermediates more akin to those in condensed-phase inorganic and organometallic chemistry. In parallel to the laboratory measurements, we perform computational modeling to compare with the experimental results. The field is widely open, and we are well positioned as a major player.

The new knowledge created from our research activities includes accurate ionization energies, metal-ligand and ligand-based vibrational frequencies, electron configurations, and molecular geometries of the chemical intermediates. The ionization energy is the minimum amount of the energy required to remove an electron from a molecular substance in the gaseous state. The ionization energy is a basic thermochemical property of a molecule and can be used to obtain the chemical bond dissociation energy. A molecular vibration is a periodic motion and the frequency of the periodic motion is known as a vibrational frequency. The metal-ligand vibrational frequencies describe how the metal and molecular fragments are connected together by chemical bonds and how strong these bonds are. The ligand-based vibrational frequencies describe the atomic connectivity and strength of the chemical bonds within a molecular fragment. The electronic configurations map out how electrons are arranged in the molecular orbitals. The electron configuration and molecular geometry together determine the chemical reactivity, physical state, and other properties of a substance. The new knowledge about reactive substances is used to devise plausible mechanisms of metal-induced chemical activation and catalysis. A catalyst is a substance that speeds up a chemical process that would otherwise be too slow to be economical for industry. Knowing the reaction mechanisms allows scientists to design new catalysts with targeted and predicable properties.

Our research activities provide technically challenging training for students and prepare them effectively for promising careers. The students gain experience in sophisticated instrumentation, advanced laser spectroscopic and imaging techniques, and modern computational chemistry. They learn skills in the design, operation, and interpretation of scientific experiments and in the presentation of research discoveries. Our research group consists of students of both genders with diverse cultural backgrounds and has ongoing national and international collaborations. This environment further enriches student experience for future employment. The students in our group have gone on successful positions in technical or educational workforce.

Our research activities have been supported by the National Science Foundation, Petroleum Research Fund of the American Chemical Society, and Kentucky Science and Engineering Foundation.

L. Wu, C. Zhang, S. A. Krasnokutski, and D. -S. Yang, "Threshold Ionization, Structural Isomers, and Electronic States of M2O2 (M=Sc, Y, and La), J. Chem. Phys. 140, 224307/1-9 (2014).

S. Kumari and D. -S. Yang, "High-Resolution Electron Spectroscopy and Rotational Conformers of Group 6 Metal (Cr, Mo, and W) Bis(mesitylene) Sandwich Complexes" (Terry Miller Festschrift), J. Phys. Chem. A 117, 13336-13344 (2013).

S. Kumari, B. Sohnlein, D. Hewage, M. Roudjane, J. Lee, and D. -S. Yang, "Binding Sites and Electronic States of Group 3 Metal-Aniline Complexes probed by High-Resolution Electron Spectroscopy," J. Chem. Phys. 138,224304/1-9 (2013).

X. Wang, J. Lee, and D. -S. Yang, "High-Resolution Electron Spectroscopy and Molecular Structures of Cu-(2,2'-bipyridine) and Cu-(4,4'-bipyridine)" (Invited article, Dennis Salahub Special Issue), Can. J. Chem. 91, 613-620 (2013).

S. Kumari, M. Roudjane, D. Hewage, Y. Liu, and D. -S. Yang, "High-Resolution Electron Spectroscopy of Lanthanide (Ce, Pr, and Nd) Complexes of Cyclooctatetraene: The role of 4f electrons," J. Chem. Phys. 138, 164307/1-9(2013).

L. Wu, C. Zhang, S. Krasnokutski, and D. –S. Yang, “Mass-Analyzed Threshold Ionization and Electronic States of M3O4 (M = Sc, Y, and La),” J. Chem. Phys. 137, 084312/1-7 (2012).

L. Wu, Y. Liu, C. Zhang, S. Li, D. A. Dixon, and D. –S. Yang, “Mass-Analyzed Threshold Ionization and Excited State of Lanthanum Dioxide,“ J. Chem. Phys. 137, 034307/1-8 (2012).

Y. Lei, L. Wu, B. R. Sohnlein, and D. –S. Yang, “High-Spin Electronic States of Lanthanum-Arene Complexes: Nd(benzene) and Nd(naphthalene),“ J. Chem. Phys. 136, 204311/1-8 (2012).

M. Roudjane, S. Kumari, and D.-S. Yang, “Electronic States and Metal-Ligand Bonding of Gadolinium Complexes of Benzene and Cyclo-octatetraene,” J. Phys. Chem. A 116, 839-845 (2012).

Y. Liu, S. Li, B. R. Sohnlein, S. Kumari, M. Roudjane, and D. –S. Yang, “Electronic States and Pseudo Jahn-Teller Distortion of Heavy Metal-Monobenzene Complexes: M(C6H6) (M = Y, La, and Lu,” J. Chem. Phys. 136, 134310/1-9 (2012).

D. –S. Yang, “High-Resolution Electron Spectroscopy of Metal-Aromatic Complexes,”J. Phys. Chem. Lett. (Perspective), 2, 25-33 (2011).

J. Lee, S. A. krasnokutski, and D. –S. Yang, “High-Resolution Electron Spectroscopy, Preferential Metal-Binding Sites, and Theromochemistry of Lithium Complexes of Polycyclic Aromatic Hydrocarbons,” J. Chem. Phys. 134, 024301/1-9 (2011).

D. –S. Yang, “Probing the Bonding and Structures of Metal-Organic Radicals with Zero Energy Electrons,” Sci. China Chem. (Special Issue: International Year of Chemistry 2011), 54 (12), 1831-1840 (2011).

J. S. Lee, Y. Lei, and D. –S. Yang, “Electron-Spin Multiplicities of Transition-Metal Aromatic Radicals and Ions: M[C6(CH3)6] and M+[C6(CH3)6] (M = Ti, V, and Co), J. Phys. Chem A, 115, 6509-6517 (2011).

N. Mirsaleh-Kohan, W. D. Robertson, R. N. Compton, S. A. Krasnokutski, and D. –S. Yang, “Ionic and Vibrational Properties of An Ultra-Low Ionization Potential Molecule: Tetrkis(dimethylamino)ethylene,” Int. J. Mass Spectrom. 304, 57-65 (2011).

Y. Liu, C. Zhang, L. Wu, S. A. Krasnokutski, and D. –S. Yang, “Electronic States and Spin-Orbit Splitting of Lanthanum Dimer,“ J. Chem. Phys. 135, 034309/1-7 (2011).

S. A. Krasnokutski, J. S. Lee, and D. –S. Yang, “High-Resolution Electron Spectroscopy and Structures of Lithium-Nucleobase (Adenine, Uracil, and Thymine) Complexes,” J. Chem. Phys.132, 044304-1/8 (2010).

J. S. Lee, S. Kumari, and D. –S. Yang, “Conformational Isomers and Isomerization of Group 6 (Cr, Mo, and W) Metal-Bis(toluene) Sandwich Complexes Probed by Variable-Temperature Electron Spectroscopy,” (Klaus Mueller-Dethlefs Festschrift Special Issue), J. Phys. Chem. A 114, 11277-84 (2010).

J. S. Lee, Y. Lei, S. Kumari, and D. –S. Yang, “Ring Deformation and p-Electron Redistribution of Methylbenzenes Induced by Metal Coordination,“ J. Phys. Chem. A 114, 9136-43 (2010).

J. S. Lee, Y. Lei, S. Kumari, and D. –S. Yang, “Metal Coordination Converts the Tub-Shaped Cyclooctatetraene into an Aromatic Molecule: Electronic States and Half-sandwich Structures of Group III Metal-Cyclooctatetraene Complexes,” J. Chem. Phys. 131, 104304-1/7 (2009).